Falling object in specific time
I guess you can either:

Make the physics begin at frame 250 in the Scene settings &gt; Rigid Body World &gt; Simulation Start:



Or you can activate the object's rigid body Animated option at frame 0, which means it won't be submited to any physic simulation, keyframe, disable it at frame 250 and keyframe again (deactivate and activate Dynamic will work as well):